Automatic Detection of Resonance Frequency of a Downhole System

ABSTRACT

A system includes a downhole tool adapted to be run at plural operating frequencies, a drive system to control an operating frequency of the downhole tool, and a controller to control the drive system to, in a test procedure, vary the operating frequency of the downhole tool. The controller automatically detects a resonance frequency of the downhole tool in the test procedure.

BACKGROUND

To produce hydrocarbons from a well, an artificial lift mechanism thatutilizes a pump is sometimes used. One type of pump is an electricalsubmersible pump that can be operated at different frequencies. Theelectrical submersible pump can be controlled by a variable speed drivesystem that is able to vary the operational frequency of the electricalsubmersible pump.

It is desired that the electrical submersible pump not be run at itsresonance frequency, as excessive vibration may occur when theelectrical submersible pump is run at the resonance frequency. Theresonance frequency of an object is the natural frequency of vibrationof the object, determined by the physical parameters of the object.

Conventionally, to identify the resonance frequency of the electricalsubmersible pump, a manual procedure is performed. The manual procedureinvolves controlling the variable speed drive system (normally locatedat the earth surface) to perform a frequency sweep of the electricalsubmersible pump. The vibration of the electrical submersible pump ismonitored by the well operator over the frequency sweep. Normally, thefrequency associated with the maximum amount of vibration is consideredthe resonance frequency, which is recorded by the well operatorconducting the test. The variable speed drive system is then manuallyset to skip the resonance frequency during normal operation of theelectrical submersible pump.

Such manual testing of the electrical submersible pump is time-consumingand labor intensive, which increases the cost of deploying a completioninto a well.

SUMMARY OF THE INVENTION

In general, a downhole system (e.g., an electrical submersible pump) canbe run at plural frequencies, and a drive system controls an operatingfrequency of the downhole system. A controller controls the drive systemto, in a test procedure, vary the operating frequency of the downholesystem, and to automatically detect a resonance frequency of thedownhole system in the test procedure. The controller is also able toset the detected resonance frequency as an operating frequency to avoid.

Other or alternative features will become apparent from the followingdescription, from the drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a system with a pump located in a wellbore and asurface variable frequency drive and control system having a module todetermine a resonance frequency of the pump, according to an embodiment.

FIG. 2 is a flow diagram of a process of detecting the resonancefrequency of the pump of FIG. 1, according to an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, numerous details are set forth to providean understanding of the present invention. However, it will beunderstood by those skilled in the art that the present invention may bepracticed without these details and that numerous variations ormodifications from the described embodiments may be possible.

As used here, the terms “up” and “down”; “upper” and “lower”; “upwardly”and downwardly”; “upstream” and “downstream”; “above” and “below”; andother like terms indicating relative positions above or below a givenpoint or element are used in this description to more clearly describesome embodiments of the invention. However, when applied to equipmentand methods for use in wells that are deviated or horizontal, such termsmay refer to a left to right, right to left, or other relationship asappropriate.

FIG. 1 illustrates a system that includes a string deployed in awellbore 100, where the string has a pump assembly 102 that is carriedon a tubing 104. In one embodiment, the pump assembly 102 is anelectrical submersible pump (ESP) assembly that is controlledelectrically to pump fluids in the wellbore 100 up to the well or earthsurface 101. The electrical submersible pump assembly 102 is an exampleof a downhole system that is capable of running at various operatingfrequencies. In other embodiments, other types of downhole systems arealso capable of running at various operating frequencies. Also, insteadof a tubing 104, other types of conveyance structures can be used forcarrying the downhole system into the wellbore 100, such as wirelines,coiled tubing, cables and so forth.

The wellbore 100 is lined by a casing or liner 106 that extends from thewell surface 101. Wellhead equipment 124 is provided at the well surface101. A wellhead penetrator 122 is provided through the wellheadequipment 124 to enable electric power transmission from a surfacevariable speed drive system 130 to the submersible pump assembly 102through the wellhead equipment 124.

According to one example, the electrical submersible pump assembly 102includes a pump 108, a motor 114 for powering the pump 108, a protector116 to prevent wellbore fluid entry into the motor, and an intake/gasseparator 112 where wellbore fluid enters the pump 108. Also, theelectrical submersible pump assembly 102 may include a gas handlingdevice 110 for handling an amount of gas that cannot be handled by thesubmersible pump, and a downhole sensor module 118 (connected toassociated transducers) for providing pressure, temperature, flow rate,current, and/or vibration readings associated with the wellbore 100 andsubmersible pump assembly 102. The components of the electricalsubmersible pump assembly 102 are provided for purposes of example, asother pump assemblies can have other components.

The motor 114 is connected to an electric cable 120 that extends throughthe wellhead equipment 124. The cable 120 further extends out from thewellhead equipment 124 to a control module 126 at the well surface 101.

The control module 126 includes a controller 128 and the variable speeddrive system 130. Note that other components (not shown) can also bepart of the control module 126. The variable speed drive system 130controls the speed at which the motor 114 runs. The speed controlaffects the operating frequency of the electrical submersible pumpassembly 102. The variable speed drive system 130 is connected to thecontroller 128, which controls (among others) the speed variationprovided by the variable speed drive system 130. The variable speeddrive system 130 also provides protection functions for the submersiblepump assembly 102.

In accordance with some embodiment of the invention, the controller 128includes a resonance frequency detection software 134 that is executableon a central processing unit (CPU) 136. The CPU 136 is connected to astorage 138 for storing data and software instructions. The resonancefrequency detection software 134 provides an automated mechanism forautomatically detecting the resonance frequency of the electricalsubmersible pump assembly 102 (or other type of downhole tool that iscapable of operating at multiple frequencies). Using the resonancefrequency detection software 134 in the controller 128 to perform theresonance frequency detection enables a well operator to automate theresonance frequency detection procedure, such that the well operatordoes not have to manually detect for the resonance frequency and to makeadjustments in the variable speed drive system 130 for such resonancefrequency. The resonance frequency detection software 134 works with anelectric submersible pump assembly 102 that includes a downhole sensormodule that is able to measure vibration at any point on the submersiblepump assembly 102.

According to some embodiments of the invention, the resonance frequencydetection software 134 is executable to detect the resonance frequencyof the electrical submersible pump assembly 102, and to automaticallyset one of the resonance frequencies that the variable speed drivesystem 130 will skip, called “setting a jump frequency.”

A user station 132 can be coupled to the control module 126. Using theuser station 132, such as a notebook computer, a desktop computer, apersonal digital assistant (PDA), or other user device, a user (such asa well operator) can invoke execution of the resonance frequencydetection software 134 as well as view the results of the execution ofresonance frequency detection software 134. Also, the user can monitoroperation of the electrical submersible pump assembly 102. All of thesecan be accomplished through the local user interface on the controlmodule 126.

In one embodiment, the user station 132 includes a user interface thatdisplays control elements to control the resonance frequency detectionsoftware 134. The user interface also displays fields for outputtingresults of a test conducted by the resonance frequency detectionsoftware 134 for determining the resonance frequency of the electricalsubmersible pump assembly 102. Optionally, the user interface in theuser station 132 can also be used to control the variable speed drivesystem 130.

The resonance frequency detection software 134 is an example of a moduleto automatically detect for a resonance frequency of a downhole systemsuch as the electrical submersible pump assembly 102. In otherembodiments, instead of being a software module, a module implemented inhardware or a combination of hardware and firmware can be used toperform automated resonance frequency detection.

According to one embodiment, to enable the test procedure for finding aresonance frequency by the resonance frequency detection software 134, adownhole sensor module 118 is provided in the electrical submersiblepump assembly 102. The downhole sensor module 118 is connected to thecable 120 through the motor 104, while one or more transducers can belocated at any point on the electrical submersible pump assembly 102.

As depicted in FIG. 2, to perform the test procedure, the resonancefrequency detection software 134 is executable to receive or generate(at 202) minimum and maximum operating frequency values that define afrequency range over which a frequency sweep is to be performed in thetest procedure. In one implementation, the minimum and maximum operatingfrequencies can be entered by a user at the user station 132 or throughthe user interface of the controller 128. For example, the userinterface presented by the resonance frequency detection software 134can have fields for receiving various parameters, including the minimumand maximum operating frequencies.

Alternatively, the minimum and maximum operating frequencies can begenerated by the resonance frequency detection software 134 based onvarious data associated with the electrical submersible pump assembly102. For example, the electrical submersible pump assembly 102 can beassociated with motor “nameplate” data, including the maximum horsepowerof the motor 114, and the motor nameplate frequency. The motor nameplatefrequency is typically 50 Hz or 60 Hz, depending on power supplyfrequency. The maximum frequency for the frequency sweep is then derivedusing the following equation: ${{Max}\quad{Freq}} = \begin{matrix}{{Motor}\quad{Nameplate}\quad{Frequency}^{*}} \\\sqrt{\begin{matrix}{{Motor}\quad{Nameplate}\quad{{HP}/{HP}}\quad{Consumption}} \\{{At}\quad{Motor}\quad{Nameplate}\quad{Frequency}}\end{matrix}\quad}\end{matrix}$

The HP consumption at motor nameplate frequency refers to the expectedhorsepower consumed by the pump 108, gas handling device 110 (ifpresent), and intake/gas separator 112 being run by the motor at themotor nameplate frequency. The HP consumption at motor nameplatefrequency can be entered by a user (such as through the user station132), or can be derived from other information such as pressure or flowrate information from transducers located on the electrical submersiblepump assembly 102.

After receiving or generating (at 202) the minimum and maximum operatingfrequencies at 102, the resonance frequency detection software 134causes (at 204) the controller 128 to control the variable speed drivesystem 130 to run the electrical submersible pump assembly 102 from theminimum operating frequency to the maximum operating frequency. Duringthis frequency sweep, the resonance frequency detection software 134receives (at 206) vibration data from a sensor.

The vibration data is stored (at 208) and correlated to the operatingfrequencies. For example, the vibration data and corresponding operatingfrequencies can be stored in a table format. Based on the receivedvibration data, the resonance frequency detection software 134determines (at 210) the resonance frequency, which is the frequency atwhich maximum vibration is detected (from the vibration data).

The detected resonance frequency is then stored (at 212) and optionallyreported to the user at the user station 132. Also, the controller 128,based on the resonance frequency determined by the resonance frequencydetection software 134, sets (at 214) the variable speed drive system130 to skip the resonance frequency. For example, the variable speeddrive system 130 can be associated with a jump frequency or jumpfrequencies that is or are to be skipped over during operation.

Instructions of the resonance frequency detection software 134 (FIG. 1)are stored on one or more storage devices in the controller 128 andloaded for execution on a processor (such as CPU 136). The processorincludes microprocessors, microcontrollers, processor modules orsubsystems (including one or more microprocessors or microcontrollers),or other control or computing devices. As used here, a “control module”refers to hardware, software, or a combination thereof. A “controlmodule” can refer to a single component or to plural components (whethersoftware or hardware).

Data and instructions (of the software) are stored in respective storagedevices, which are implemented as one or more machine-readable storagemedia. The storage media include different forms of memory includingsemiconductor memory devices such as dynamic or static random accessmemories (DRAMs or SRAMs), erasable and programmable read-only memories(EPROMs), electrically erasable and programmable read-only memories(EEPROMs) and flash memories; magnetic disks such as fixed, floppy andremovable disks; other magnetic media including tape; and optical mediasuch as compact disks (CDs) or digital video disks (DVDs).

While the invention has been disclosed with respect to a limited numberof embodiments, those skilled in the art, having the benefit of thisdisclosure, will appreciate numerous modifications and variationstherefrom. It is intended that the appended claims cover suchmodifications and variations as fall within the true spirit and scope ofthe invention.

1. An apparatus comprising: a downhole system adapted to be run atplural operating frequencies; a drive system to control an operatingfrequency of the downhole tool; and a controller to control the drivesystem to, in a test procedure, vary the operating frequency of thedownhole system, the controller to automatically detect a resonancefrequency of the downhole system in the test procedure.
 2. The apparatusof claim 1, the controller to further set the detected resonancefrequency as a frequency to avoid in the drive system.
 3. The apparatusof claim 2, wherein the controller sets the detected resonance frequencyto avoid by setting the resonance frequency as a jump frequency in thedrive system.
 4. The apparatus of claim 1, wherein the controllercomprises a central processing unit and software executable on thecentral processing unit, the software executable to perform the controland detect tasks.
 5. The apparatus of claim 1, wherein the downholesystem comprises a pump adapted to be run at the plural operatingfrequencies.
 6. The apparatus of claim 5, wherein the pump comprises anelectrical submersible pump.
 7. The apparatus of claim 1, furthercomprising a vibration sensor to detect vibration of the downhole systemduring the test procedure, the controller to receive data from thevibration sensor for detecting the resonance frequency.
 8. The apparatusof claim 7, the controller to perform the test procedure by causing theoperating frequency of the downhole tool to be varied across apredefined frequency range.
 9. The apparatus of claim 1, furthercomprising at least one of a user station and a local user interface ofthe controller to display a result of the test procedure.
 10. A methodto perform a test procedure in a downhole tool deployed in a wellbore,comprising: varying, in response to control of a control module, anoperating frequency of the downhole tool across a predefined frequencyrange in the test procedure; receiving, by the control module, vibrationdata of the downhole tool as the operating frequency of the downholetool is varied across the predefined frequency range; and automaticallydetermining, by the control module, a resonance frequency of thedownhole tool based on the vibration data.
 11. The method of claim 10,further comprising displaying a result of the test procedure on a userinterface.
 12. The method of claim 10, further comprising setting, at adrive system that controls the operating frequency of the downhole tool,a frequency to avoid based on the determined resonance frequency. 13.The method of claim 10, wherein varying the operating frequency of thedownhole tool comprises varying the operating frequency of an electricalsubmersible pump.
 14. The method of claim 10, wherein receivingvibration data of the downhole tool comprises receiving vibration datafrom a vibration sensor in the downhole tool.
 15. The method of claim14, further comprising receiving a minimum operating frequency and amaximum operating frequency that defines the predefined frequency range.16. The method of claim 15, further comprising generating the maximumoperating frequency based at least in part on flow rate information orpressure information received from one or more sensors in the downholetool.
 17. An article comprising at least one storage medium containinginstructions that when executed cause a control module to: control adrive system to vary an operating frequency of a downhole tool across apredefined frequency range during a test procedure; and determine aresonance frequency of the downhole tool based on information receivedfrom the downhole tool during the test procedure as the operatingfrequency of the downhole tool is varied across the predefined frequencyrange.
 18. The article of claim 17, wherein the instructions whenexecuted cause the control module to further receive vibration data froma vibration sensor of the downhole tool, wherein determining theresonance frequency of the downhole tool is based on the vibration data.19. The article of claim 17, wherein the instructions when executedfurther cause the control module to generate a maximum operatingfrequency of the predefined frequency range, the maximum operatingfrequency generated based on flow rate information or pressureinformation received from one or more sensors of the downhole tool. 20.The article of claim 19, wherein generating the maximum operatingfrequency is further based on horsepower information of the downholetool.
 21. The article of claim 17, wherein controlling the drive systemto vary the operating frequency of the downhole tool comprisescontrolling the drive system to vary the operating frequency of a pumpassembly.